The production of sub-micrometer (100 nm&lt;diameter&lt;1 .mu.m) and nano-scale (1 nm&lt;diameter&lt;100 nm) particles has received attention in both basic science and advanced technology research. There is a growing interest in producing clusters and nano-scale crystalline material for potential catalytic, sensor, aerosol, filter, biomedical, magnetic, dielectric, magnetic structural, opto-electronic structural, ceramics and metallurgical applications. This is because nano-scale particles exhibit volume effects and surface effects absent in the same material with dimensions in the micrometer range. Nano-scale particles have unique physical properties (e.g. optical, dielectric, magnetic, mechanical), transport properties (e.g., thermal, atomic diffusion) and processing characteristics (e.g., faster sintering kinetics, super-plastic forming).
The nano-scale particles provide a narrow size distribution which is required to obtain a uniform material response. Materials such as paints, pigments, electronic inks and ferrofluids as well as advanced functional and structural ceramics require that the particles be uniform in size and stable against agglomeration. Fine particles, particularly nano-scale particles with significant surface area often agglomerate to minimize total surface or interfacial energy of the system. Although the process of using solution chemistry can be a practical route for the synthesis of both submicrometer and nano-scale particles of many materials, issues such as the control of size, distribution of particles, morphology and crystallinity, particle agglomeration during and after synthesis and separation of these particles from the reactant needs further investigation.
The usual synthesis techniques for producing nano-scale particles include mechanical milling of solid phases, solution chemistry and vapor-phase synthesis. Nano-scale structured particles have also been synthesized by chemical techniques such as chemical precipitation, and sol-gel processing. Also, vapor deposition of nano-scale particles has been achieved by gas evaporation, laser ablation and sputtering. Each of the mentioned synthesis techniques provides its own particular specific advantages, but they also have the following individual disadvantages which require the search for an improved process for producing nano-scale particles. Mechanical milling allows contamination to the particles and a particle size of less than 100 nm can not be produced. Solution chemistry, vapor phase synthesis, chemical precipitation, sol-gel processing and vapor deposition are processes that are very slow and are difficult to control in order to acquire a desired size and shape of the nano-scale particles to be produced. Many of these synthesis techniques also require the use of a vacuum unit and involve environmental concerns about chemical waste disposal.
Nanocrystalline materials find many applications in chemical, biological, metallurgical, electronic and ceramic industry. For example, nano-crystalline silver particles are used in the fabrication of solder paste, dental paste, thick film conductors for electronic circuits, jet printer and high speed photographic films. Nano-clusters of ruthenium are used as a seed for the nucleation and growth of organic molecules for DNA analysis. Nanometer sized palladium clusters are often used as catalysts and advanced electronic materials. Nano-clusters of cobalt are used in magnetic recording media and in the construction of permanent magnets.
It is an objective of the present invention to increase the quality and synthesis rate of nano-scale particles by laser-liquid interaction. It is also the objective of the present invention to provide improved control of the size of nano-scale particles to be produced. It is further the objective of the present invention to provide and apparatus and process to produce nano-scale particles that are more economical, cost effective and environmentally compliant.